Laboratory researchers have been presented with a major R&D challenge with antibiotic-resistant bacteria. Fortunately, a solution to this problem is readily available now.
Going beyond Pasteur – the benefits and growing application of the calorimetry approach in the field
The development of antibiotic-resistant compounds has mainly adopted the traditional Pasteur-style microbiology approach – predominantly involving culturing, plating and manual operation. The fundamental problems with molecular-based, non-culture methods, which invariably rely on DNA typing or proteomics, are threefold - they are often costly, have low specificity and are unable to differentiate between living, dead, and highly persistent dormant bacteria. What the R&D community has lacked until recently is a sensitive, label-free cell-based assay possessing the capability to measure bacterial activity in real time with the minimal effort. As a consequence, scientists, committed to the development of innovative solutions, went beyond Pasteur to find an alternative that provides the effective solution that the industry has been after. The answer is calorimetry and advanced technology that brings the application of this effective approach to life.
Calorimetry-based microbial measurements
The calorimetry-based monitoring of living systems had fallen out of use, until recently, due to an industry perception that the approach is too complex. However, demand has been fuelled for calorimetry from a combination of the pressing and high priority need to tackle antibiotic resistance, together with technological advancement. Calorimetry-based cell monitoring, with the accuracy of the data it generates, are uniquely suited to the development of novel antibiotics.
The calorimetry approach, brought into operation through advanced technologies that are now available, provides researchers and clinicians dealing with bacterial infections with tests that are both accurate and at the same time fast – serving as a highly reliable scientific tool for determining whether an antibiotic should be used in the patient, the type of antibiotic to utilize and the choice of therapy to apply.
At its core, calorimetry measures the power produced in a cell culture at any given time as Joules/second (W). The heat generated is a measure of the metabolic processes in the cells and, as a consequence, gives a true phenotype fingerprint of the organism measured. Different bacteria and treatments create unique heat profiles that reveal significant information about the system being tested. Calorimetry provides a label-free, non-destructive measurement - making post experimental analysis possible, whilst being independent of sample morphology. This means that assays can be performed both on bacteria in solution as well as on solid media, including three-dimensional matrices such as surgical and dental implant materials and bone biopsies
One of the unique properties of calorimetry-based metabolic monitoring of bacterial growth is that the pattern of energy expenditure is species, as well as strain, specific - over time, each bacterium gives rise to a specific growth pattern as heat production. This can be used to quantify the number of bacteria and to determine the species. The bacterial load determination is similar to a quantitative PCR measurement, in which the curves are identical in shape, but different numbers of cycles are needed to reach the detection limit. Furthermore, different loads of bacteria require a varying number of cell divisions to reach the detection limit concerned. The metabolic output assay therefore becomes quantitative as well as qualitative. Minor changes in growth behaviour, such as metabolic pathway mutations, are detected, as are biofilm formation and, most significantly, antimicrobial sensitivity.
Through integrating the metabolic power over time to accumulated heat over time (in Joules), a growth curve is established equivalent to a traditional growth curve (as measured by optical density ...
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